JP5082203B2 - Water-based ink, method for producing water-based ink, ink jet printer, and ink jet recording method - Google Patents

Description

  The present invention relates to a water-based ink, particularly a water-based ink used in an ink-jet method, a method for producing a water-based ink, an ink-jet printer, and an ink-jet recording method. The present invention relates to a method, an ink jet printer, and an ink jet recording method.

  In recent years, the ink jet recording system can create images easily and inexpensively, and thus has been applied to various printing fields such as photographs, various printing, marking, and special printing such as color filters. In particular, ink jet recording devices that emit and control fine dots, ink with improved color reproduction gamut, durability, and emission suitability, ink absorbency, coloring material color development, surface gloss, etc. are dramatically improved. It is also possible to obtain image quality comparable to silver halide photography using special paper.

  However, in an inkjet image recording system that requires dedicated paper, there are problems in that the recording media that can be used are limited and the cost of the recording media is increased.

  On the other hand, in the office, there is an increasing need for a system capable of performing full color printing at high speed without being restricted by a recording medium (for example, plain paper, coated paper, art paper, etc.).

  In particular, it is desired to perform high-quality printing at high speed on plain paper (for example, PPC paper, non-coated paper for printing, etc.) that is inexpensive and easily available. There are problems such as blurring of characters and images, low reflection density, curling after printing, and cockling. Further, when performing double-sided printing, back-through (print-through) is also a major issue. In order to solve such problems of plain paper printing, various studies have been conducted including the composition of water-based ink.

  As one of the improvement methods for the above problem, a technique for improving image bleeding and ink back-through when printing on plain paper by using a water-based ink containing vinylpyrrolidone having a molecular weight equivalent to 80,000 to 250,000 and an acrylic acid copolymer. Is disclosed (for example, see Patent Document 1). However, in this method, when the water-based ink adhering to the nozzle plate is wiped off by the wiping operation, the added ultra-high molecular weight polymer tends to stick to the nozzle plate, so that wiping residue is likely to occur. There has been a problem that image deterioration is likely to occur due to a deviation in the landing positions of the droplets.

  As another method, a technique for reducing feathering, bleeding, and back-through during printing on plain paper using an aqueous ink containing alginic acid or alginate is disclosed (for example, see Patent Document 2). This method improves feathering, bleeding, and strike-through by reacting alginic acid or alginate contained in water-based ink with polyvalent metal cations such as calcium and aluminum contained in plain paper to cause gelation and thickening. It is said that. However, polyvalent metal ions such as calcium and aluminum in plain paper are not essential components, but are contained as impurities. The content varies depending on the brand of the paper, and some of the plain paper has extremely low content. Exists. Therefore, the magnitude of these effects depends on the brand of paper to be printed, and there is a problem that a sufficient effect cannot be obtained depending on the brand of paper.

  In addition, a technique for improving the sharpness at the time of printing on plain paper by using an aqueous ink containing colloidal silica having an average particle diameter of 5 to 100 nm and a pigment is disclosed (for example, see Patent Document 3). However, in order to obtain sufficient sharpness by this method, it is necessary to add a large amount of colloidal silica, and it is a problem that the emission stability such as intermittent emission (decapability) deterioration and nozzle clogging is easily lost. It was.

  Further, there is a technique for reducing color bleed in plain paper printing by discharging a colorless liquid composition containing a cationic polymer having an average molecular weight of 400 to 1400 and a colored aqueous ink with separate heads and combining them on paper. (For example, refer to Patent Document 4). However, this method requires a head for discharging colorless liquid. Further, there is a problem that paper cockling and curling are likely to occur due to an increase in the total amount of liquid recorded on the paper by the amount of the colorless liquid composition.

  On the other hand, in an oil-based ink composition with almost no curling or cockling, it contains 10% or more of a solvent (nonpolar solvent) having a 50% distillation point of 280 ° C. or lower, and a solvent (polar solvent, ester) of 300 ° C. or higher. A technique for improving bleeding after recording by containing 20% or more of a (system solvent) is disclosed (for example, see Patent Document 5). However, even with this method, the reflection density, behind-the-scenes, and character reproducibility are not necessarily at sufficient levels.

Based on the above, the technology that balances the image quality such as character image quality, blurring, reflection density, and back-through, which are the issues of inkjet image recording on plain paper, and the curling and cockling issues has not been realized yet. is there.
Japanese Patent Laid-Open No. 10-1629 JP 2003-176432 A JP-A-9-227812 JP-A-10-95107 Japanese Patent Laid-Open No. 2004-2666

  The object of the present invention has been made in view of the above-mentioned problems, and the object is that the emission from an inkjet head and the ink storage stability are good, the image density when printed on plain paper, the resistance to see-through and the characters. An object of the present invention is to provide a water-based ink excellent in quality, curl resistance and cockling resistance, a method for producing the same, an ink jet printer using the water-based ink, and an ink jet recording method.

  The above object of the present invention is achieved by the following configurations.

(Claim 1)
At least water, a water-soluble organic solvent, a colorant, and a metal oxide colloid, and the total amount of the water-soluble organic solvent is 50% by mass or more and less than 90% by mass of the total mass of the ink. , Containing a water-soluble organic solvent having an SP value of 8 or more and less than 12 in an amount of 30% by mass or more of the total mass of the ink, and the content of the solid component of the metal oxide colloid is 0.1% by mass or more of the total mass of the ink; It is less than 10% by mass, and the metal oxide colloid is a bead-shaped metal oxide colloid satisfying all of the following conditions (1) to (3), and the total amount of alkali metals is less than 500 ppm. Water-based ink.
Condition (1): (secondary average particle diameter) / (primary average particle diameter) is 3.0 or more and less than 30
Condition (2): The primary average particle diameter is 10 nm or more and less than 80 nm.
Condition (3): secondary average particle size of 40 nm or more and less than 300 nm
(Claim 2)
The water-based ink according to claim 1, wherein the metal oxide colloid is beaded colloidal silica.
(Claim 3)
At least water, a water-soluble organic solvent, a colorant, and a metal oxide colloid, and the total amount of the water-soluble organic solvent is 50% by mass or more and less than 90% by mass of the total mass of the ink. A method for producing a water-based ink comprising a water-soluble organic solvent having an SP value of 8 or more and less than 12 in an amount of 30% by mass or more of the total mass of the ink and a total amount of alkali metals of less than 500 ppm, comprising the metal oxide The colloid is a bead-shaped metal oxide colloid satisfying all of the following conditions (1) to (3), the total amount of alkali metals per 1% by mass of the metal oxide colloid is less than 50 ppm, and the metal oxidation A method for producing a water-based ink, wherein the solid colloid is added so that the content of the solid component of the product colloid is 0.1% by mass or more and less than 10% by mass of the total mass of the ink.
Condition (1): (secondary average particle diameter) / (primary average particle diameter) is 3.0 or more and less than 30
Condition (2): The primary average particle diameter is 10 nm or more and less than 80 nm.
Condition (3): secondary average particle size of 40 nm or more and less than 300 nm
(Claim 4)
At least water, a water-soluble organic solvent, a colorant, and a metal oxide colloid, and the total amount of the water-soluble organic solvent is 50% by mass or more and less than 90% by mass of the total mass of the ink. The water-soluble organic solvent having an SP value of 8 or more and less than 12 is contained at 30% by mass or more of the total mass of the ink, the total amount of alkali metals is less than 500 ppm, and the content of the solid component of the metal oxide colloid is The water-based ink is a bead-shaped metal oxide colloid that is 0.1% by mass or more and less than 10% by mass of the total mass of the ink, and the metal oxide colloid satisfies all of the following conditions (1) to (3). A method for producing a water-based ink, wherein the dispersion of the colorant uses an anionic polymer dispersant, and the anionic polymer dispersant is neutralized with an organic base. Method.
Condition (1): (secondary average particle diameter) / (primary average particle diameter) is 3.0 or more and less than 30
Condition (2): The primary average particle diameter is 10 nm or more and less than 80 nm.
Condition (3): secondary average particle size of 40 nm or more and less than 300 nm
(Claim 5)
The method for producing a water-based ink according to claim 3 or 4, wherein the metal oxide colloid is beaded colloidal silica.
(Claim 6)
An ink jet printer having an ink jet head having a nozzle diameter of 25 μm or less and emitting the water-based ink according to claim 1 or 2 from the nozzle.
(Claim 7)
The nozzle having a diameter of 25 μm or less has a line head type ink jet head in which a plurality of nozzles are arranged in a direction intersecting with the conveyance direction of the recording medium, and substantially does not scan the ink jet head. An ink jet printer, wherein the water-based ink described is emitted from the nozzle and recorded.
(Claim 8)
An ink jet recording method comprising printing on both sides of plain paper using the ink jet printer according to claim 6.

  According to the present invention, the emission from an ink jet head and ink storage stability are good, the image density when printed on plain paper, the through-through resistance and the character quality are excellent, and the curl resistance and cockling resistance are also excellent. An aqueous ink and a method for producing the same, an ink jet printer using the aqueous ink, and an ink jet recording method can be provided.

  Hereinafter, the best mode for carrying out the present invention will be described in detail.

  As a result of intensive studies in view of the above problems, the present inventor contains at least water, a water-soluble organic solvent, a colorant and a metal oxide colloid, and the total amount of the water-soluble organic solvent is 50% by mass of the total mass of the ink. As described above, the water-soluble organic solvent having an SP value of 8 or more and less than 12 among the water-soluble organic solvents is 30% by mass or more of the total mass of the ink, and the total amount of Lucari metal is 500 ppm. The water-based ink, which is characterized by being less than, has good light emission from the inkjet head, provides high image density when printed on plain paper, is excellent in showthrough resistance and character quality, and curl resistance As a result, it has been found that a water-based ink excellent in cockling resistance and a water-based ink excellent in letter-through resistance and character quality can be realized.

  In general, when ink having a high water content in ink such as water-based ink is recorded on plain paper, the penetration into the paper is not so high, and a moderate character image quality and extremely low showthrough characteristics are obtained. It is done.

  However, when printing on plain paper with water-based ink having a high water content, there is a problem that the curl becomes very large. This is because the water in the ink is coordinated to the cellulose fibers constituting the plain paper, so that the penetration is small, and for curls, a force in the shrinking direction works by evaporating and drying the water, but in the case of water-based ink It is considered that curling occurs as a result of insufficient force for suppressing drying shrinkage because water bonds to cellulose to release bonds between cellulose.

  On the other hand, for example, when oil-based ink that does not contain water is recorded on plain paper, the penetration of the ink into the plain paper is large, resulting in a decrease in surface image density and a large amount of ink penetration. This is thought to be because the interaction between the oily solvent and cellulose is small, and the oily solvent easily diffuses through the gaps between the cellulose, so that the penetration increases, the image density decreases, and the showthrough increases. On the other hand, since the coordination to cellulose is small and the bond between celluloses is not broken, the paper structure before recording is maintained, and it is considered that curling is difficult.

  In the water-based ink of the present invention, the total amount of the water-soluble organic solvent is 50% by mass or more and less than 90% by mass of the total mass of the ink, and the water-soluble organic solvent having an SP value of 8 or more and less than 12 among the water-soluble organic solvents. The first feature is that it contains 30% by mass or more of the total ink. With this organic solvent composition, it is possible to obtain a print having excellent character image quality, small show-through, and almost no curling even when recorded on plain paper. Furthermore, the effect of achieving both character image quality, back-through and curl suppression is completely deviated from the trend of water-based ink and oil-based ink.

  As a manifestation mechanism of this effect, the total amount of the water-soluble organic solvent is 50 mass% or more and less than 90 mass% of the total mass of the ink, and among the water-soluble organic solvents, the SP value is 8 or more and less than 12. Is contained in an amount of 30% by mass or more of the total mass of the ink, and further contains at least water, thereby reducing the interaction between the ink and the cellulose fiber, and the amount of inter-cellulose bonds necessary to resist drying shrinkage even after recording. It is considered that curling is suppressed by making it remain, and that there is a portion that interacts with cellulose by containing water, though it is small, so that character image quality and show-through are good.

  In addition, the ink of the present invention has a second feature that it uses a colorant (specifically, a pigment or colored fine particles) and contains a metal oxide colloid as an additive. By adding this metal oxide colloid, it becomes possible to further improve the effect of preventing the show-through and improve the character image quality, and further improve the surface reflection density. In particular, a bead-shaped metal oxide colloid in which the metal oxide colloid has the following shape can be particularly preferably used.

  As shown in FIG. 1, a metal oxide colloid is deposited on a paper fiber, and pigment particles or colored fine particles having a finite size are deposited therewith, whereby a pigment is formed near the surface of the paper. As a result, it is considered that the effect of preventing the show-through and the character image quality and the effect of improving the surface reflection density were obtained.

  Further, the ink of the present invention is characterized in that the total amount of alkali metals (lithium, sodium, potassium) in the ink is less than 500 ppm, more preferably 1 ppm or more and less than 300 ppm. By making the total amount of alkali metals in the ink less than 500 ppm, the total amount of the water-soluble organic solvent is 50% by mass or more of the total mass of the ink, and among the water-soluble organic solvents, the water-soluble organic having an SP value of 8 or more and less than 12. It has been found that the metal oxide colloid and the pigment dispersion can be more stably present even in a solvent composition containing 30% by mass or more of the total mass of the ink and further containing at least water.

  Alkali metals in aqueous inks are often brought in as salts of surfactants or pigment dispersants or contained in metal oxide colloidal solutions. Therefore, in order to control the alkali metal, ion exchange water is naturally used at the time of ink production. When a surfactant is used in addition to this, a nonionic surfactant is used. As the dispersant used for dispersing the pigment, a dispersant neutralized with an organic base is used. The metal oxide colloid is added to the ink as an acid state metal oxide colloid having a small alkali metal content. It is preferable to combine these methods.

  In order to obtain such a water-based ink, a method of adding a metal oxide colloid as an acidic metal oxide colloid with a low alkali metal content, or a surfactant for dispersing a colorant, and a salt of an organic base. It is a more preferable embodiment to use a combination of the method of adding as a.

  Details of the present invention will be described below.

  In the aqueous ion of the present invention, the solvent composition contains at least water, and the total amount of the water-soluble organic solvent is 50% by mass or more and less than 90% by mass of the total mass of the ink. The water-soluble organic solvent having an SP value of 8 or more and less than 12 is 30% by mass or more of the total mass of the ink. Furthermore, the water-soluble organic solvent having an SP value of 8 or more and less than 10 is preferably 30% by mass or more of the total mass of the ink.

The solubility parameter (SP value) of the water-soluble organic solvent referred to in the present invention is a value represented by the square root of the molecular aggregation energy, and is described in Polymer Handbook (Second Edition) Chapter IV Solubility Parameter Values. Use. The unit is (J / cm ³ ) ^1/2 and refers to the value at 25 ° C. In addition, about what does not have description of data, it can calculate by calculating | requiring evaporation heat from a boiling point.

  Examples of water-soluble organic solvents corresponding to SP values of 8 or more and less than 12 are shown below and their SP values (shown by numerical values in parentheses), but the present invention is not limited to this. Absent.

Ethylene glycol monomethyl ether (11.6)
Ethylene glycol monoethyl ether (11.4)
Ethylene glycol monobutyl ether (9.8)
Ethylene glycol monoisopropyl ether (9.2)
Ethylene glycol monoisobutyl ether (8.9)
Diethylene glycol monomethyl ether (11.6)
Diethylene glycol monoethyl ether (11.2)
Diethylene glycol monobutyl ether (9.5)
Diethylene glycol monoisobutyl ether (8.7)
Diethylene glycol dimethyl ether (9.4)
Triethylene glycol monomethyl ether (10.5)
Triethylene glycol monoethyl ether (10.4)
Triethylene glycol monobutyl ether (9.6)
Propylene glycol monomethyl ether (10.4)
Propylene glycol monobutyl ether (8.9)
Propylene glycol monophenyl ether (9.4)
Dipropylene glycol monomethyl ether (9.6)
Dipropylene glycol monobutyl ether (8.2)
Dipropylene glycol monophenyl ether (8.6)
Tripropylene glycol monomethyl ether (9.1)
In the present invention, in addition to the water-soluble organic solvent having an SP value of 8 or more and less than 12, various water-soluble organic solvents are used in combination, and the total amount of the water-soluble organic solvent is 50% by mass or more and less than 90% by mass of the total amount of the ink. can do. Below, the example of the water-soluble organic solvent applicable by this invention is shown.

  Examples of water-soluble organic solvents preferably used include alcohols (eg, methanol, ethanol, propanol, isopropanol, butanol, isobutanol, secondary butanol, tertiary butanol, pentanol, hexanol, cyclohexanol, benzyl alcohol, etc.), Polyhydric alcohols (for example, ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycol, propylene glycol, dipropylene glycol, polypropylene glycol, butylene glycol, hexanediol, pentanediol, glycerin, hexanetriol, thiodiglycol, 1,3 -Propanediol, 1,4-butanediol, 1,5-pentanediol, 1,2-pentanediol 1,2-hexanediol, 1,2,6-hexanetriol, etc.), amines (eg, ethanolamine, diethanolamine, triethanolamine, N-methyldiethanolamine, N-ethyldiethanolamine, morpholine, N-ethylmorpholine, ethylenediamine) , Diethylenediamine, triethylenetetramine, tetraethylenepentamine, polyethyleneimine, pentamethyldiethylenetriamine, tetramethylpropylenediamine, etc.), amides (eg, formamide, N, N-dimethylformamide, N, N-dimethylacetamide, etc.), Heterocycles (eg, 2-pyrrolidone, N-methyl-2-pyrrolidone, cyclohexyl pyrrolidone, 2-oxazolidone, 1,3-dimethyl-2-imidazolidinone), sulfo Kishido compound (such as dimethyl sulfoxide, etc.), sulfones (e.g., sulfolane), urea, acetonitrile, and acetone.

  Examples of the metal oxide colloid used in the water-based ink of the present invention include colloidal silica, alumina sol, and zirconia sol. Of these, colloidal silica is particularly preferable.

  The secondary average particle diameter of the metal oxide colloid is preferably less than 300 nm. The shape is preferably a bead-shaped metal oxide colloid that satisfies all of the following conditions (1) to (3) rather than a spherical shape.

Condition (1): (Secondary average particle diameter) / (Primary average particle diameter) is 3.0 or more and less than 30 Condition (2): Primary average particle diameter is 10 nm or more and less than 80 nm Condition (3): Secondary average The particle diameter is 40 nm or more and less than 300 nm The bead shape referred to in the present invention refers to a shape connected in a linear or planar shape, not a three-dimensional mass such as a so-called lump. This shape can be observed with an electron microscope.

  The primary particles referred to in the present invention refer to individual particles constituting the bead-like metal oxide colloidal particles, and the particle diameter can be determined by observation with an electron microscope. The average particle size can be obtained by performing particle image photographing on at least 100 particles and statistically processing the image using image analysis software such as Image-Pro (manufactured by Media Cybernetics). Is possible.

  The primary average particle diameter of the inorganic fine particles according to the present invention is preferably 10 nm or more and less than 80 nm, as defined in the condition (2). When the primary average particle diameter is less than 10 nm, the dispersion stability of the colorant is remarkably deteriorated, and when it is 80 nm or more, the reflection density of the printed matter is lowered. A more preferable range of the primary average particle diameter is 10 nm or more and less than 30 nm.

  Moreover, the secondary particle as used in the field of this invention refers to the structure where the said primary particle was connected in the shape of a bead, and the particle diameter can be calculated | required by the measurement by a dynamic light scattering method.

  The secondary average particle size of the inorganic fine particles according to the present invention is preferably 40 nm or more and less than 300 nm, as defined by the condition (3). If the secondary average particle diameter is less than 40 nm, the image bleeding resistance and the effect of preventing the see-through are insufficient, and if it is 300 nm or more, clogging in the ink jet head is likely to occur. A more preferable range of secondary average particle diameter is 100 nm or more and less than 200 nm.

  In the present invention, the ratio of the primary average particle diameter to the secondary average particle diameter [(secondary average particle diameter) / (primary average particle diameter)] is 3.0 or more as defined in the condition (1), Preferably it is less than 30. If this ratio is less than 3.0, the image bleeding resistance and the effect of preventing the see-through are insufficient, and if it is 30 or more, clogging in the ink jet head tends to occur. The ratio of the primary average particle diameter to the secondary average particle diameter is more preferably 5.0 or more and less than 20.

  Moreover, it is preferable that the bonds of the primary particles forming the secondary particles are bonded by a covalent bond rather than a relatively weak bond such as van der Waals force or hydrogen bond force.

  Examples of the bead-like metal oxide colloid used in the present invention include Snowtex ST-UP, PS-SO, and PS-MO (manufactured by Nissan Chemical Co., Ltd.).

  Various known methods can be used as the method for producing the bead-like inorganic fine particles, and for example, it can be produced by the method described in World Patent No. 00/15552.

  The content of the bead-like metal oxide colloid according to the present invention is characterized in that it is 0.1% by mass or more and less than 10% by mass as a solid content with respect to the total amount of the water-based ink. 3 mass% or more and 5.0 mass%. If the content of the bead-like inorganic fine particles is less than 0.1% by mass, the effect of preventing image bleeding and back-through is insufficient, and if it is 10% by mass or more, the stability of the aqueous ink is deteriorated.

  One feature of the water-based ink of the present invention is that it contains a colorant. The colorant as used in the present invention refers to a pigment or colored fine particles. Combined with the effect of the inorganic fine particles as defined in the present invention by the solid pigment or colored fine particles, the effect of blurring and see-through in ordinary paper recording can be obtained. In the aqueous ink of the present invention, the content of the pigment or colored fine particles is preferably 0.1% by mass or more and less than 12% by mass with respect to the total mass of the aqueous ink.

  The colored fine particles preferably used in the present invention are those containing a dye as a colorant in polymer fine particles such as acrylic acid and dispersed in a solvent. As the dye, an oily dye is frequently used, and a dye that is soluble in an organic solvent having no water-soluble group such as carboxylic acid and sulfonic acid and insoluble in water, such as a disperse dye, is usually selected. Also included are dyes that exhibit oil solubility by salting a water-soluble dye with a long-chain base. For example, acid dyes, direct dyes, salt-forming dyes of reactive dyes and long-chain amines are known. .

  As the pigment that can be used in the present invention, conventionally known pigments can be used without particular limitation, and any of water-dispersible pigments, solvent-dispersible pigments, and the like can be used, for example, organic pigments such as insoluble pigments and lake pigments, An inorganic pigment such as carbon black can be preferably used. The pigment is present in a dispersed state in the water-based ink. The dispersion method may be any of self-dispersion, activator dispersion, polymer dispersion, and microcapsule dispersion, but the polymer dispersion and microcapsule dispersion are fixed. From the viewpoint of sex.

  The insoluble pigment is not particularly limited, for example, azo, azomethine, methine, diphenylmethane, triphenylmethane, quinacridone, anthraquinone, perylene, indigo, quinophthalone, isoindolinone, isoindoline, azine, oxazine, thiazine, Dioxazine, thiazole, phthalocyanine, diketopyrrolopyrrole and the like are preferable.

  Specific pigments that can be preferably used include the following pigments.

  Examples of the magenta or red pigment include C.I. I. Pigment red 2, C.I. I. Pigment red 3, C.I. I. Pigment red 5, C.I. I. Pigment red 6, C.I. I. Pigment red 7, C.I. I. Pigment red 15, C.I. I. Pigment red 16, C.I. I. Pigment red 48: 1, C.I. I. Pigment red 53: 1, C.I. I. Pigment red 57: 1, C.I. I. Pigment red 122, C.I. I. Pigment red 123, C.I. I. Pigment red 139, C.I. I. Pigment red 144, C.I. I. Pigment red 149, C.I. I. Pigment red 166, C.I. I. Pigment red 177, C.I. I. Pigment red 178, C.I. I. And CI Pigment Red 222.

  Examples of the pigment for orange or yellow include C.I. I. Pigment orange 31, C.I. I. Pigment orange 43, C.I. I. Pigment yellow 12, C.I. I. Pigment yellow 13, C.I. I. Pigment yellow 14, C.I. I. Pigment yellow 15, C.I. I. Pigment yellow 15: 3, C.I. I. Pigment yellow 17, C.I. I. Pigment yellow 74, C.I. I. Pigment yellow 93, C.I. I. Pigment yellow 128, C.I. I. Pigment yellow 94, C.I. I. And CI Pigment Yellow 138.

  Examples of the pigment for green or cyan include C.I. I. Pigment blue 15, C.I. I. Pigment blue 15: 2, C.I. I. Pigment blue 15: 3, C.I. I. Pigment blue 16, C.I. I. Pigment blue 60, C.I. I. And CI Pigment Green 7.

In addition to the above pigments, when red, green, blue, or intermediate colors are required, the following pigments are preferably used alone or in combination. I. Pigment Red; 209, 224, 177, 194,
C. I. Pigment Orange; 43,
C. I. Vat Violet; 3,
C. I. Pigment Violet; 19, 23, 37,
C. I. Pigment Green; 36, 7,
C. I. Pigment Blue; 15: 6,
Etc. are used.

  Examples of black pigments include C.I. I. Pigment black 1, C.I. I. Pigment black 6, C.I. I. Pigment black 7 and the like.

  The average particle diameter of the colorant dispersion used in the aqueous ink of the present invention is preferably 50 nm or more and less than 200 nm. If the average particle size of the colorant dispersion is less than 50 nm or 200 nm or more, the stability of the colorant dispersion tends to be poor, and the storage stability of the aqueous ink tends to deteriorate.

  The particle size measurement of the colorant dispersion can be obtained by a commercially available particle size measuring instrument using a dynamic light scattering method, an electrophoresis method or the like. The accuracy of is well used.

  The pigments or colored fine particles used in the present invention are preferably dispersed by a disperser and used together with a dispersant and other additives necessary for various desired purposes. As the disperser, a conventionally known ball mill, sand mill, line mill, high-pressure homogenizer, or the like can be used. Among them, the dispersion by sand mill is preferable because the particle size distribution is sharp when the dispersion is aimed at an average particle diameter of around 100 nm. The material of the beads used for sand mill dispersion is preferably zirconia or zircon from the viewpoint of contamination of bead fragments and ionic components. Further, the bead diameter is preferably 0.1 mm or more and 0.5 mm.

  Examples of the polymer dispersant for dispersing the pigment or colored fine particles according to the present invention include higher fatty acid salts, alkyl sulfates, alkyl ester sulfates, alkyl sulfonates, sulfosuccinates, naphthalene sulfonates, and alkyl phosphates. , Polyoxyalkylene alkyl ether phosphate, polyoxyalkylene alkyl phenyl ether, polyoxyethylene polyoxypropylene glycol, glycerin ester, sorbitan ester, polyoxyethylene fatty acid amide, amine oxide and other activators, or styrene, styrene derivatives Block consisting of two or more monomers selected from vinyl naphthalene derivatives, acrylic acid, acrylic acid derivatives, maleic acid, maleic acid derivatives, itaconic acid, itaconic acid derivatives, fumaric acid, fumaric acid derivatives. Copolymers, may be mentioned random copolymers and salts thereof.

  In the present invention, the addition amount of the colorant dispersant is preferably 10 to 100% by mass with respect to the colorant.

  In the dispersion of the colorant according to the present invention, a surfactant can be used as an additive. As the surfactant used in the present invention, any of cationic, anionic, amphoteric and nonionic surfactants can be used, but it is particularly preferable to use a nonionic surfactant from the viewpoint of dispersion stability.

  Nonionic activators include, for example, polyoxyethylene secondary alcohol ether, polyoxyethylene alkylphenyl ether, polyoxyethylene sterol ether, polyoxyethylene lanolin derivative polyoxyethylene polyoxypropylene alkyl ether, polyoxyethylene glycerin fatty acid ester , Polyoxyethylene castor oil, hydrogenated castor oil, polyoxyethylene sorbitol fatty acid ester, polyethylene glycol fatty acid ester, fatty acid monoglyceride, polyglycerin fatty acid ester, sorbitan fatty acid ester, propylene glycol fatty acid ester, sucrose fatty acid ester, fatty acid alkanolamide, poly Oxyethylene fatty acid amide, polyoxyethylene alkylamine, alkylamine oxide , Acetylene glycol, acetylene alcohol, and the like.

  In the water-based ink of the present invention, in addition to the above description, if necessary, according to the purpose of improving the emission stability, the compatibility with the print head and the ink cartridge, the storage stability, the image storage stability, and other various performances. Various additives such as polysaccharides, viscosity modifiers, specific resistance regulators, film forming agents, ultraviolet absorbers, antioxidants, anti-fading agents, anti-fouling agents, rust inhibitors, etc. For example, oil droplet fine particles such as liquid paraffin, dioctyl phthalate, tricresyl phosphate, silicone oil, ultraviolet absorbers described in JP-A-57-74193, 57-78988 and 62-261476, JP-A-57-74192, 57-87989, 60-72785, 61-146591, JP-A-1-95091 and 3-13376, etc. Fluorescent whitening agents described in JP-A-59-42993, JP-A-59-52689, JP-A-62-280069, JP-A-6-2422871, and JP-A-4-219266 Etc.

  In the water-based ink of the present invention having the above-described configuration, the surface tension of the water-based ink is preferably 25 to 40 mN / m at 25 ° C., more preferably 25 to 35 mN / m, still more preferably 30 to 35 mN. / M. Further, the viscosity of the water-based ink is preferably 1 to 40 mPa · s at 25 ° C., more preferably 5 to 40 mPa · s, and further preferably 5 to 20 mPa · s.

  Further, the dissolved oxygen concentration in the aqueous ink of the present invention is preferably 2 ppm or less at 25 ° C. By setting this dissolved oxygen concentration condition, the formation of bubbles can be suppressed, and emission is also possible in high-speed printing. An ink jet recording method having excellent stability can be realized. As a method for measuring the dissolved oxygen dissolved in the ink, for example, it can be measured using a dissolved oxygen measuring device DO-14P (manufactured by Toa Radio).

  In the ink jet recording method of the present invention, printing is performed on both sides of a recording paper using the water-based ink of the present invention.

  The plain paper used in the present invention is not particularly limited, and its constitution is mainly composed of chemical pulp, sizing agent and filler represented by LBKP and NBKP, and other paper making aids are used as necessary. Paper was made by law. As the pulp material used for the plain paper according to the present invention, mechanical pulp and recycled paper recycled pulp may be used in combination, and there is no problem even if these are used as the main material.

  Examples of the sizing agent internally added to the plain paper according to the present invention include rosin size, AKD, Alnicel succinic anhydride, petroleum resin-based size, epichlorohydrin, cationic starch, and acrylamide.

  Examples of the filler internally added to the plain paper according to the present invention include finely divided silicic acid, aluminum silicate, diatomaceous earth, kaolin, kaolinite, halloysite, nalite, dickite, pyrophyllite, sericite, titanium dioxide, bentonite and the like. Is mentioned.

  In the ink jet recording method using the water-based ink of the present invention, for example, an ink jet print is obtained by ejecting ink as droplets from an ink jet head based on a digital signal and adhering to plain paper with a printer loaded with ink jet ink. It is done.

  When forming an image by ejecting the ink of the present invention, the ink jet head to be used may be an on-demand system or a continuous system. In addition, as a discharge method, an electro-mechanical conversion method (for example, a single cavity type, a double cavity type, a bender type, a piston type, a shear mode type, a shared wall type, etc.), an electro-thermal conversion method (for example, thermal ink jet) Any ejection method such as a mold, a bubble jet (registered trademark) mold, or the like may be used.

  Among them, as an ink jet printer used in the ink jet recording method of the present invention, the aqueous ink of the present invention is ejected from an ink jet head having a nozzle diameter of 25 μm or less, preferably 1 μm or more and 25 μm or less, and recording is performed on a recording medium. Alternatively, recording is performed on a recording medium by discharging from a line head type inkjet head having a nozzle diameter of 25 μm or less, preferably 1 μm or more and 25 μm or less. In addition, the ink jet recording system of the present invention is characterized in that image printing is performed on both sides of plain paper.

  In double-sided printing, after printing on one side, plain paper is turned over and transported with the printing side down. However, the water-based ink of the present invention has the above-mentioned characteristics. Since there is no bleeding of characters and characters, high density and excellent character quality on any surface, no conveyance failure occurs, and the conveyance belt is not contaminated with aqueous ink.

  EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto. In addition, although the display of "part" or "%" is used in an Example, unless otherwise indicated, "part by mass" or "mass%" is represented.

<< Preparation of dispersant solution >>
As a dispersant, John Crill 678 (manufactured by Johnson Polymer), a neutralizer, tripropylene glycol monmethyl ether (TPGME) and water were mixed with stirring at a mass ratio shown in Table 1 to prepare dispersant solutions 1 to 4. .

<< Preparation of pigment dispersion >>
After mixing the pigment, solvent, dispersant solution, and ion-exchanged water in the combinations shown in Table 2, the mixture was sealed in a polypropylene plastic bottle with 200 g of zirconia beads having a diameter of 0.5 mm, and 5 hours in a paint shaker. Dispersion was performed to obtain black pigment dispersions A to G.

  The details of each pigment described in Table 2 are as follows.

MA7: Mitsubishi Carbon Black MA7 (Mitsubishi Chemical Corporation)
MA100: Mitsubishi Carbon Black MA100 (Mitsubishi Chemical Corporation)
MA600: Mitsubishi Carbon Black MA600 (Mitsubishi Chemical Corporation)

<< Preparation of water-based ink >>
The following solvent, water, surfactant, antifungal agent, additive and colloidal silica were mixed and stirred, and pigment dispersions A to G prepared by the above method were added and stirred well. Subsequently, this liquid was filtered with a # 3500 mesh metal filter, deaerated with a hollow fiber membrane, and water-based inks 1 to 21 were prepared.

Colloidal silica dispersion (see below for types and solids concentrations listed in Table 3)
Addition amount shown in Table 3 Pigment dispersion (type shown in Table 3) 20.0 parts (colorant 3.0%)
Solvent (types listed in Table 3) Addition amount listed in Table 3 Surfactant: Olphin E1010 (manufactured by Nissin Chemical) Addition amount listed in Table 3 Antifungal agent: Proxel GXL (manufactured by Avicia) 0.20 Part After mixing each of the above additives, water was added to finish to 100 parts.

  The details of each additive described in abbreviations in Table 3 are as follows.

<solvent>
DPGME: Dipropylene glycol monomethyl ether TPGME: Tripropylene glycol monomethyl ether TEGBE: Triethylene glycol monobutyl ether GLY: Glycerin DEG: Diethylene glycol EG: Ethylene glycol <Colloidal silica dispersion>
PS-MO: manufactured by Nissan Chemical Co., Ltd., beaded colloidal silica PS-MO (average primary particle size: 22 nm, sodium ion content 220 ppm, solid content concentration 18%)
PS-SO: manufactured by Nissan Chemical Co., Ltd., beaded colloidal silica PS-SO (average primary particle size: 13 nm, sodium ion content 260 ppm, solid content concentration 15%)
ST-OUP: manufactured by Nissan Chemical Co., Ltd., beaded colloidal silica PS-OUP (average primary particle size: 20 nm, sodium ion content 100 ppm, solid content concentration 16%)
ST-OL: manufactured by Nissan Chemical Co., Ltd., colloidal silica PS-OL (average primary particle size: 45 nm, sodium ion content 230 ppm, solid content concentration 20%)
ST-ZL: manufactured by Nissan Chemical Co., Ltd., colloidal silica PS-ZL (average primary particle size: 85 nm, sodium ion content 500 ppm, solid content concentration 40%)
PS-S: manufactured by Nissan Chemical Co., Ltd., beaded colloidal silica PS-S (average primary particle size: 13 nm, sodium ion content 1500 ppm, solid content concentration 20%)
ST-UP: manufactured by Nissan Chemical Co., Ltd., beaded colloidal silica PS-UP (average primary particle size: 20 nm, sodium ion content 1800 ppm, solid content concentration 20%)
<Characteristic evaluation of water-based ink>
[Quantification of alkali metal salt in water-based ink]
The amount of alkali metal in each of the prepared water-based inks was measured by an atomic absorption method.

(Evaluation of light emission)
The prepared water-based inks 1 to 21 were continuously ejected from a share mode piezo-type inkjet head having a nozzle diameter of 20 μm and a number of nozzles of 256 nozzles under a discharge condition of a droplet amount of 7 pl and a drive frequency of 15 kHz for 1 minute. The discharge state was visually observed, and the emission property was evaluated according to the following criteria.

○: Discharge is good with all 256 nozzles Δ: Flying bend occurs with 1 to 10 nozzles x: Flying bend occurs with 11 or more nozzles Or, one or more missing nozzles were generated. [Evaluation of ink storage stability]
The prepared water-based inks 1 to 21 were put in a polypropylene container, sealed, and stored at 60 ° C. for 1 week. Each water-based ink after storage is ejected from a share mode piezo-type ink jet head with a nozzle diameter of 20 μm and a number of nozzles of 256 nozzles under the conditions of a droplet volume of 7 pl and a drive frequency of 15 kHz. The ink storage stability was evaluated according to

◯: Good ejection with all 256 nozzles Δ: Missing occurred with 1 nozzle ×: Missing with 2-10 nozzles xx: Unable to emit at all << Inkjet image recording >>
[Image recording A]
A piezo type of a line head type in which the nozzle diameter is 25 μm, the number of nozzles is 512, and the nozzle resolution is 600 dpi (in the present invention, dpi represents the number of dots per 2.54 cm). Using a line head printer equipped with a recording head, water-based inks 1 to 21 on J paper (64 g / m ² , A4 size) manufactured by Konica Minolta Business Technology Co., Ltd. on a condition of recording resolution of 600 × 600 dpi Data J1 was printed on one side to create images 1A to 21A.

[Image recording B]
Using the same line head printer as image recording A, Konica Minolta Business applied water-based inks 1 to 21 under the conditions of a recording resolution of 600 × 600 dpi and an ink adhesion amount of 10 ml / m ² and an image size of 200 × 280 mm. A solid image on one side of Technology J paper (64 g / m ² , A4 size), in a room with a temperature of 23 ° C and a relative humidity of 50% 1B to 21B were created.

[Image recording C]
A solid image is printed on both sides of J paper (64 g / m ² , A4 size) manufactured by Konica Minolta Business Technology Co., Ltd. under the same conditions as image recording B, and the room temperature is 23 ° C. and relative humidity is 50%. Then, the printed surface was laid flat for 1 day and dried to prepare images 1C to 21C.

[Evaluation of recorded images]
The following evaluations were performed on each of the created images.

(Evaluation of surface concentration)
About each image created by the image recording B, the amber density was measured on the printed surface side with a reflection densitometer (status A), and rank evaluation was performed as follows.

○: Reflection density is 1.2 or more Δ: Reflection density is 1.0 or more and less than 1.2 ×: Reflection density is less than 1.0
The amber density was measured with a reflection densitometer (status A) on the printed surface and the back surface of each image created in image recording B, and the strikethrough rate was calculated according to the following formula to evaluate the rank.

Back-through rate (%) = (reflection density on the back surface) / (reflection density on the printed surface) × 100
○: Back-through rate is less than 15% Δ: Back-through rate is 15% or more and less than 20% ×: Back-through rate is 20% or more (Evaluation of character quality)
The characters of JEIDA standard pattern data J1 printed in image record A were visually observed, and the following rank evaluation was performed.

○: Character outline is clear, density is high and easy to read △: Character outline blurring and details are crushed, but reading is possible as a whole ×: Character outline blurring is large, density is also Low and difficult to read as a whole (evaluation of curl resistance)
About each sample created by image recording B and image recording C, the curl state was measured and the following rank evaluation was performed.

○: Neither the image B nor the image C is lifted at the end of 5 mm or more in height, and the occurrence of cockling is not observed. Δ: Both the images B and C are at the end of 5 mm or more in height There is no part floating, but at least one of the images has cockling (皺). X: At least one of the images B and C is lifted at the end of 5 mm or more in height, and the cockling ( Table 4 shows the results obtained as described above.

  As is clear from the results shown in Table 4, water, a water-soluble organic solvent, a colorant and a metal oxide colloid are contained, and the total amount of the water-soluble organic solvent is 50% by mass or more and less than 90% by mass of the total mass of the ink. Among the water-soluble organic solvents, the water-based ink of the present invention containing a water-soluble organic solvent having an SP value of 8 or more and less than 12 in an amount of 30% by mass or more of the total mass of the ink It can be seen that the ink storage stability is excellent, a high image density, a low strike-through rate are obtained, and the character quality and curl resistance are excellent.

It is a schematic diagram which shows the state at the time of discharging the aqueous ink containing the bead-like metal oxide colloid and coloring agent which concern on this invention to the plain paper which consists of paper fibers.

Claims (6)

Contains at least water, a water-soluble organic solvent, a colorant and a metal oxide colloid,
The total amount of the water-soluble organic solvent is 50% by mass or more and less than 90% by mass of the total mass of the ink;
Among the water-soluble organic solvents, a water-soluble organic solvent having an SP value of 8 or more and less than 12 is contained at 30% by mass or more of the total mass of the ink,
The content of the solid component of the metal oxide colloid is 0.1% by mass or more and less than 10% by mass of the total mass of the ink,
The water-based ink, wherein the metal oxide colloid is a bead-shaped colloidal silica that satisfies all of the following conditions (1) to (3), and the total amount of alkali metals is less than 500 ppm.
Condition (1): (Secondary average particle diameter) / (Primary average particle diameter) is 3.0 or more and less than 30 Condition (2): Primary average particle diameter is 10 nm or more and less than 80 nm Condition (3): Secondary average Particle size is 40nm or more and less than 300nm At least water, a water-soluble organic solvent, a colorant, and a metal oxide colloid, and the total amount of the water-soluble organic solvent is 50% by mass or more and less than 90% by mass of the total mass of the ink. A method for producing a water-based ink comprising a water-soluble organic solvent having an SP value of 8 or more and less than 12 in an amount of 30% by mass or more of the total mass of the ink and a total amount of alkali metals of less than 500 ppm,
The metal oxide colloid is a bead-shaped colloidal silica that satisfies all of the following conditions (1) to (3):
The total amount of the alkali metal per 1% by mass of the metal oxide colloid is less than 50 ppm, and the content of the solid component of the metal oxide colloid is 0.1% by mass or more and less than 10% by mass of the total mass of the ink. A method for producing a water-based ink, characterized by comprising:
Condition (1): (Secondary average particle diameter) / (Primary average particle diameter) is 3.0 or more and less than 30 Condition (2): Primary average particle diameter is 10 nm or more and less than 80 nm Condition (3): Secondary average Particle size is 40nm or more and less than 300nm At least water, a water-soluble organic solvent, a colorant, and a metal oxide colloid, and the total amount of the water-soluble organic solvent is 50% by mass or more and less than 90% by mass of the total mass of the ink. The water-soluble organic solvent having an SP value of 8 or more and less than 12 is contained at 30% by mass or more of the total mass of the ink, the total amount of alkali metals is less than 500 ppm, and the content of the solid component of the metal oxide colloid is Production of water-based ink, which is 0.1% by mass or more and less than 10% by mass of the total mass of the ink, and the metal oxide colloid is a bead-shaped colloidal silica that satisfies all of the following conditions (1) to (3). A method,
A method for producing a water-based ink, characterized in that an anionic polymer dispersant is used for dispersion of the colorant, and the anionic polymer dispersant is neutralized with an organic base.
Condition (1): (Secondary average particle diameter) / (Primary average particle diameter) is 3.0 or more and less than 30 Condition (2): Primary average particle diameter is 10 nm or more and less than 80 nm Condition (3): Secondary average Particle size is 40nm or more and less than 300nm An inkjet printer having an inkjet head having a nozzle diameter of 25 μm or less and emitting the water-based ink according to claim 1 from the nozzle. The nozzle according to claim 1 , wherein the nozzle having a diameter of 25 μm or less has a line head type inkjet head in which a plurality of nozzles are arranged in a direction intersecting a conveyance direction of the recording medium, and substantially does not scan the inkjet head. An ink jet printer, wherein water-based ink is emitted from the nozzle and recorded. 6. An ink jet recording method comprising printing on both sides of plain paper using the ink jet printer according to claim 4 .

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